Metabolically engineered Escherichia coli for efficient production of glycosylated natural products

Significant achievements in polyketide gene expression have made Escherichia coli one of the most promising hosts for the heterologous production of pharmacologically important polyketides. However, attempts to produce glycosylated polyketides, by the expression of heterologous sugar pathways, have been hampered until now by the low levels of glycosylated compounds produced by the recombinant hosts. By carrying out metabolic engineering of three endogenous pathways that lead to the synthesis of TDP sugars in E. coli, we have greatly improved the intracellular levels of the common deoxysugar intermediate TDP-4-keto-6-deoxyglucose resulting in increased production of the heterologous sugars TDP-L-mycarose and TDP-D-desosamine, both components of medically important polyketides. Bioconversion experiments carried out by feeding 6-deoxyerythronolide B (6-dEB) or 3-α-mycarosylerythronolide B (MEB) demonstrated that the genetically modified E. coli B strain was able to produce 60- and 25-fold more erythromycin D (EryD) than the original strain K207-3, respectively. Moreover, the additional knockout of the multidrug efflux pump AcrAB further improved the ability of the engineered strain to produce these glycosylated compounds. These results open the possibility of using E. coli as a generic host for the industrial scale production of glycosylated polyketides, and to combine the polyketide and deoxysugar combinatorial approaches with suitable glycosyltransferases to yield massive libraries of novel compounds with variations in both the aglycone and the tailoring sugars.